Traffic Links

Ramp Meters

On I-405 in Renton, ramp meters provided a travel times savings of 3 to 16 minutes.

Ramp meters are a proven and cost-effective method of relieving traffic congestion.

Why is WSDOT adding new ramp meters? These time-tested tools that help reduce highway congestion have long been used in King and Snohomish counties. During summer 2015, a series of ramp meters will be activated (pdf 252kb) along Interstate 5 between State Route 510 and State Route 512. The work is part of the WSDOT project to install "smart highway" devices along I-5 between Lacey and Lakewood.

What are ramp meters? Ramp meters are stop-and-go traffic signals that control the frequency with which vehicles enter the flow of traffic on the freeway.

Why does WSDOT install ramp meters? WSDOT uses ramp meters to reduce accidents and decrease travel times for commuters. Most ramp meters allow only one vehicle through each green light, creating a 4 to 15 second delay between cars entering the highway. This delay helps reduce disruptions to freeway traffic and reduces accidents that occur when vehicles merge onto the highway.

How do I use them? Drive your vehicle up to the white line, or stop bar, to trigger the ramp meter. If the light is red, stop at the white line. When the light turns green, merge onto the freeway. If there is a high occupancy vehicle (HOV) bypass lane, buses, carpools and vanpools do not have to stop at the ramp meter signal. They have the right of way over vehicles merging into traffic from the metered lane.

Where can I find ramp meters? The majority of ramp meters are located on our busiest highways – I-5, SR 520, I-90, I-405 and SR 167. Typically, ramps are metered from 6 a.m. to 9 a.m. and from 3 p.m. to 7 p.m. These times may vary depending on the level of traffic congestion.

Why are they effective? Without ramp meters, multiple cars try to merge simultaneously. Drivers on the freeway slow down to allow the cars enter and these slower speeds quickly cause backups. If cars enter the highway in controlled intervals, they are less likely to cause a disruption to the traffic on the freeway. A short wait on the ramp allows drivers to increase their average freeway speed and shorten overall freeway travel times. Ramp meters also reduce the number of accidents that often occur when multiple vehicles merge onto the highway at the same time.

How do ramp meters work? Ramp meters are part of a large computer-operated system that is managed in WSDOT's Traffic Management Centers (TMCs). Magnetic "loops" are embedded in the pavement that provide the TMCs with information about traffic flow, such as the volume and speed of vehicles on freeways and ramps. This traffic data is continually fed to the ramp meters, which automatically alter their cycles to maximize traffic flow on both the ramps and the freeways.